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Silly ?--probably asked before/can't find answer in Archives

Posted: Wed Nov 19, 2003 10:37 pm
by Kelly Burke Makuch
I'm fairly sure the answer to this question is yes, but I just wanted to be safe. Can I sandblast--etch on tempered glass? No great carving or any thing--just basically want to mask out an area and frost glass. The glass is approx.6-8mm thick. Thanks in advance ! Greatly appreciated!
Kelly Burke Makuch

Posted: Wed Nov 19, 2003 10:44 pm
by Tony Serviente
As long as it's just a surface etch it'll be OK.

Posted: Wed Nov 19, 2003 10:48 pm
by Kelly Burke Makuch
Thanks Tony! I thought so --better to be safe than..... Kel

Posted: Wed Nov 19, 2003 11:27 pm
by Rebecca M.
I read this article on the subject in Glass Craftsman mag. It was the last (most recent) issue.

Posted: Thu Nov 20, 2003 2:27 am
by Dean Hubbard
I was very surprised to see what that article said about this matter.
Twenty some odd years ago, when I first got into sandblasting on glass, I had a glazing manual for the apprentice program for the state of California, that said you could safely etch to a depth of 1/32" on tempered glass regardless of what thickness it was. At that time or some time shortly afterwards a craze hit in my area, many people wanted sandblasted designs put on their car windows, mainly tempered back glasses. I did several without any trouble, then one day a previous client came to me and said his back glass just popped for no apparent reason. I made him another one and sent him on his way, all was well.
A few years later I had a surface etched tempered bath enclosure break in my shop for no apparent reason, it had been setting on a glass rack for about three weeks, after I had blasted it.
I don't sandblast on tempered glass anymore. You can get away with it, but I believe, once you surface etch it, it can "go" at any time. I don't mean to rain on your parade, but I have seen many failures and I'm not talking about people that didn't know the risk of it breaking. If I need tempered glass with a design etched onto it, I do the sandblasting first then have it tempered. One company I use will even let me carve to a depth of half the thickness of the glass. If I want to protect the etched surface form the "oily fingerprint peole", I laminate it and put the etched surface towards the interlayer side. When laminating, the etching does need to be sealed first with a primer, otherwise the design would become almost invisible when the resin interlayer came in contact with it.
If you must sandblast your design on existing tempered glass, I would recomend using the finest grit you can find and go very, very light with the sandblaster.

etch on temp. glass

Posted: Thu Nov 20, 2003 8:40 am
by scooter riegelsperger
Sorry, but I agree w/ Dean. When glass is heat tempered the stucture of the outer surfaces are where the tempering takes place. It only penetrates a few thousanths of an inch. Even a .005-.010 deep scratch significantly reduces the strength. A 1/32 deep etch is really asking for trouble. It might stand up for a while but temperature change or any flexing of the part could make it shatter. Chemical tempering offers a little deeper ionic change in the outer structure but still would be significantly weakened by a 1/32" etch. I took some 3" dia. X 3/8" thick tempered windows I have and sand blasted approx. 1/32" deep line across
& then looked at part in a polariscope. The tempering pattern was changed dramatically. Then went back & tried to sb the other surface. The part shattered within seconds.

Posted: Thu Nov 20, 2003 10:55 am
by Bert Weiss
I understand a few things about this issue. The figure that I have been given is 10% of the thickness of the glass is the max you can go. I've done a surface frost with no problems that I ever heard about.

While I've seen conflicting numbers regarding strength, I was once told that tempering increases the glass's strength by 5 - 7 times. Scratching the surface with a sandblast cuts that right in half.

There are no code restrictions on sandblasting tempered glass. Probably because it will still break in small square pieces.

You can sandblast and then temper. You can even sand carve and then temper.

You can silk screen or spray Ferro frosted organic bottle coatings and fire in to 400ºF on tempered glass and get a good result.

Posted: Thu Nov 20, 2003 11:05 am
by Tony Serviente
For me, surface etching means less than a 32nd. I don't have the ability to measure how deep, but I'm guessing it's a few thousandths.